Hydrodynamic separation of grain and stover components in corn silage

Mixing fresh silage in water resulted in partial segregation of grain from stover. Grain concentration was 75% in the sunk material when silage was relatively dry (64% moisture content [MC]) and 41% when silage was relatively wet (74% MC). Partial drying to remove 20 percentage units of moisture prior to water separation increased grain concentration to 92%, and complete drying increased grain concentration to 99%. Sieving without drying followed by water separation resulted in a grain concentration of 79%. A byproduct of water separation is a large amount of soluble and deposited fine particles in the effluent: 18% of original dry matter after one separation, and between 21 and 26% after eight separations. In an industrial setting, hydrodynamic separation of silage with minimal pretreatment could provide a feedstock with a high concentration of grain (75–80%). In a laboratory setting, hydrodynamic separation with prior oven drying could provide a method to separate grain from stover in corn silage by reaching a grain concentration higher than 99%. Contribution number 761, Soils and Crops Research and Development Centre, AAFC.     

Optimization of dilute-acid pretreatment of corn stover using a high-solids percolation reactor

We have previously demonstrated that pretreatment of corn stover with dilute sulfuric acid can achieve high digestibility and efficient recovery of hemicellulose sugars with high yield and concentration. Further improvement of this process was sought in this work. A modification was made in the operation of the percolation reactor that the reactor is preheated under atmospheric pressure to remove moisture that causes autohydrolysis. This eliminated sugar decomposition during the preheating stage and led to a considerable improvement in overall sugar yield. In addition, liquid throughput was minimized to the extent that only one reactor void volume of liquid was collected. This was done to attain a high xylose concentration in the hydrolyzate. The optimum reaction and operating conditions were identified wherein near quantitative enzymatic digestibilities are obtained with enzyme loading of 15 FPU/g glucan. With a reduced enzyme loading of 5 FPU/g glucan, the enzymatic digestibility was decreased, but still reached a level of 92%. Decomposition of carbohydrates was extremely low as indicated by the measured glucan and xylan mass closures (recovered sugar plus unreacted) which were 98% and 94%, respectively. The data obtained in this work indicate that the digestibility is related to the extent of xylan removal.     

Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility

Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million to fcorn stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40% of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time, and pH during steam pretreatment. The best conditions (200°C, 5 min, 2% H₂SO₄) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated material. However, steam pretreatment at 190°C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars, 56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the glucose to ethanol efficiently.     

Effect of corn stover concentration on rheological characteristics

Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested.     

Effect of sulfuric and phosphoric acid pretreatments on enzymatic hydrolysis of corn stover

The pretreatment of corn stover with H₂SO₄ and H₃PO₄ was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H₂SO₄ pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H₃PO₄. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose removal than to delignification.     

Production of ethanol from cellulosic biomass hydrolysates using genetically engineered saccharomyces yeast capable of cofermenting glucose and xylose

Recent studies have proven ethanol to be the idael liquid fuel for transportation, and renewable ligno cellulosic materials to be the attractive feed stocks for ethanol fuel production by fermentation. The major fermentable sugars from hydrolysis of most cellulosic biomass are D-glucose and D-xylose. The naturally occurring Saccharomyces yeasts that are used by industry to produce ethanol from starches and cane sugar cannot metabolize xylose. Our group at Purdue University succeded in developing genetically engineered Saccharomyces yeasts capable of effectively cofermenting glucose and xylose to ethanol, which was accomplished by cloning three xylose-metabolizing genes into the yeast. In this study, we demonstrated that our stable recombinant Sacharomyces yeast, 424A (LNH-ST), which contains the cloned xylose-metabolizing genes stably integrated into the yeast chromosome in high copy numbers, can efficiently ferment glucose and xylose present in hydrolysates from different cellulosic biomass to ethanol.     

Impact of fluid velocity on hot water only pretreatment of corn stover in a flowthrough reactor

Flowthrough pretreatment with hot water only offers many promising features for advanced pretreatment of biomass, and a better understanding of the mechanisms responsible for flowthrough behavior could allow researchers to capitalize on key attributes while overcoming limitations. In this study, the effect of fluid velocity on the fate of total mass, hemicellulose, and lignin was evaluated for hot water only pretreatment of corn stover in tubular flow through reactors. Increasing fluid velocity significantly accelerated solubilization of total mass, hemicellulose, and lignin at early times. For example, when fluid velocity was increased from 2.8 to 10.7 cm/min, xylan removal increased from 60 to 82% for hot water only pretreatment of corn stover at 200°C after 8 min. At the same time, lignin removal increased from 30 to 46%. Dissolved hemicellulose was almost all in oligomeric form, and solubilization of hemicellulose was always accompanied by lignin release. The increase in removal of xylan and lignin with velocity, especially in the early reaction stage, suggests that chemical reaction is not the only factor controlling hemicellulose hydrolysis and that mass transfer and other physical effects may also play an important trole in hemicellulose and lignin degradation and removal.     

Hydrolysis characteristics of tissue fractions resulting from mechanical separation of corn stover

Corn stover has potential as a resource for both fiber and chemical needs if separation strategies can be developed to deal with its heterogeneity. Relative hydrolysis characteristics were assessed for pith (sclerenchyma and parenchyma) and fiber (collenchyma) tissue fractions derived from mechanical separation of corn stover to determine whether classification by tissue type resulted in fractions with different hydrolysis response. The physical characteristics of the tissue fractions were analyzed. The hydrolysis behavior of the fractions was evaluated under both acidic and basic conditions. The results from the hydrolysis experiments are compared with previously reported compositional analysis for the tissue fractions.     

电膜法生产木糖醇工艺

电膜法生产木糖醇工艺黄玉秀（华南理工大学应用化学系广州５１０６４１）关键词木糖，木糖醇，制备，电还原法１９９６－０９－１０收稿，１９９７－０１－２３修回目前生产木糖醇都用高压加氢法［１，２］．此法工艺流程长，对设备要求高，生产不安全．应用电膜法生产木...     

Ammonia fiber explosion treatment of corn stover

Optimizing process conditions and parameters such as ammonia loading, moisture content of biomass, temperature, and residence time is necessary for maximum effectiveness of the ammonia fiber explosion process. Approximate optimal pretreatment conditions for corn stover were found to be temperature of 90°C, ammonia: dry corn stover mass ratio of 1∶1, moisture content of corn stover of 60% (dry weight basis), and residence time (holding at target temperature), of 5 min. Approximately 98% of the theoretical glucose yield was obtained during enzymatic hydrolysis of the optimal treated corn stover using 60 filter paper units (FPU) of cellulase enzyme/g of glucan (equal to 22 FPU/g of dry corn stover). The ethanol yield from this sample was increased up to 2.2 times over that of untreated sample. Lowering enzyme loading to 15 and 7.5 FPU/g of glucan did not significantly affect the glucose yield compared with 60 FPU, and any differences between effects at different enzyme levels decreased as the treatment temperature increased.